1. Field of the Invention
The present invention relates to a concentrated liquid detergent composition having an excellent low-temperature stability and capable of maintaining a homogeneous phase when thawed after frozen.
2. Description of the Background Art
Owing to the wider popularity in recent years of small, light weight, compact products for household use such as detergents, smaller, more compact types of powdery heavy duty detergents and softeners comprising higher concentration active components are achieving greater sales. In spite of a great deal of advantage in small-volume products of dishwashing detergents, shampoos, etc. because of their everyday use, there are few concentrated, small-volume products on the market.
Liquid detergent compositions conventionally comprise as a major detergent component anionic surface active agents which are superior in their detergency and foaming capability. They further comprise nonionic or amphoteric surface active agents as an auxiliary agent for supplementing the detergency and foaming capability, and for decreasing irritation to the skin. Beside detergency and foaming capability, characteristics demanded of liquid detergent compositions include low-temperature stability, i.e., the outward appearance should not change and the liquid should be stably maintained when the detergent compositions are exposed to a low temperature.
Increasing the concentration of surface active agents in a liquid detergent composition, however, impairs the stability of the composition and makes the liquid composition turbid during storage at a low temperature. If such a liquid detergent composition is once frozen at a temperature below -10.degree. C., the liquid becomes turbid when thawed and does not restore its original transparency until the temperature is raised above 10.degree. C. To eliminate this problem, a hydrotroping agent such as ethanol, urea, and the like is added. However, a large amount of hydrotroping agent must be added to a liquid detergent composition containing a surface active agent at a concentration of 40% by weight or more. This causes problems such as increased flammability, objectionable odors, disagreeable foams produced by the composition, an increase in the pH during passage of time, and the like. In addition, a sufficient result in the transparency recovery of the frozen composition could not be obtained by the addition of a hydrotroping agent.
In view of the situation, the present inventors have undertaken extensive studies and found that a high-concentration liquid detergent composition comprising an anionic surface active agent and nonionic or amphoteric surface active agent at a specific ratio, and further comprising specific types of succinic acid derivative and lower alkylbenzenesulfonate, was stable at a low temperature and maintained a homogeneous phase when frozen and restored to the liquid state. Such findings have led to the completion of the present invention.